Previous studies of urban population composition by sociologists and demographers, although providing a wealth of descriptive information about urban socio-spatial characteristics, have been relatively uninformed by the more recent work of economists and urban geographers on the theoretical distribution of population groups within the metropolitan area. At the same time, these latter researchers often have not empirically tested their deductions or have ignored consideration of detailed demographic characteristics of urban residents. Substantial gain for scientific knowledge and a great deal of information relevant to current issues in national urban and population policy can derive from a careful marriage of the empirical and theoretical aspects of these disciplines. Particular research applications are proposed in the following areas: (1) changing residential distribution by occupation, income and other selected demographic characteristics; (2) cross-sectional and longitudinal analysis of urban population and land rent density gradients; (3) changing patterns of racial and ethnic segregation and assimilation; (4) location and identification of community boundaries with emphasis on distribution and change in pockets of poverty and blight; and (5) analysis of journey to work by major workplace location and socioeconomic status. The CFSC has assembled all the census tract data for metropolitan areas of the U.S. 1940-1970 and a good deal of related computer software. Thus precise tests of longstanding hypotheses of urban population distribution will be possible on a longitudinal and crosssectional basis.